Ignition coils are used in internal combustion engines for producing high voltage required for igniting the air-fuel mixture in the engine cylinders through spark plugs.
Generally, an ignition coil has a primary winding, which receives the input from an external source and a secondary winding, which steps up the source voltage, usually of the order of few hundred volts to several kilo volts.
Typically the primary winding consists of 50-300 turns and secondary winding 3000˜30,000 turns of insulated conductor depending on the specific requirement. A magnetic circuit core connects the primary winding and secondary winding.
Since the secondary winding has a large number of turns and produces high voltage, usually of the order of 10˜60 kilo volts, the winding needs to be adequately insulated, so that a winding at a lower potential does not come into contact with a winding at a potential much higher than the insulation between the two.
The required insulation is generally provided in two steps. In the first step, the windings are segregated or isolated from one another and in the second step; the windings are impregnated under vacuum process to increase the insulation to withstand the high voltage achieved by the winding during operation.
One of the well known types of windings used in industry is where the secondary winding is built segment by segment on a plastic former. Here, the segments are separated by the flanges of the plastic bobbin. Thus the windings are segregated by segments and the insulation is increased by entrapment of insulating material, generally, epoxy or varnish, during the vacuum process used conventionally.
One of the major failure modes associated with the known bobbin winding is caused due to poor adhesion of the insulating material with the plastic material of the bobbin. If the adhesion is poor, which can happen due to vacuum process variations or by long usage, voltage breakdown occurs through the interface between bobbin and winding.
Thus there exists a need for a means to eliminate the failure of the ignition coil caused by the poor adhesion of the insulating material with the plastic bobbin. Further, it is desirable to replace the material of the bobbin to a more suitable insulating material that overcomes all the shortcomings of using plastic as the insulating material.